The use of in vivo microdialysis as a tool to study neurochemical events in intact animals continues to be investigated. Experiments to validate a quantitative model of microdialysis have been carried out. Validation of this quantitative model will permit direct determination of pharmacokinetics of exogenously administered agents in extracellular fluid, as well as metabolic rate constants in intact animals for endogenous substances (neurotransmitters and metabolites). Studies to examine signal transduction in intact animals have been carried out, and receptor (beta-adrenergic) and nonreceptor (forskolin and cholera toxin) stimulated adenylate cyclase activity have been measured. Chronic lithium treatment has been shown to increase basal adenylate cyclase while blunting beta-adrenoceptor stimulated adenylate cyclase activity in intact animals.